Why the Men in Black? Why not the Men in ecru? Or the Men in aubergine? Men in technicolor?

While we can see the advantages to some of those colors—a technicolor suit would be seriously awesome—black's the proper choice for a clandestine organization with the objective to hide the truth about extraterrestrial activity on the planet.

What do we associate with black? Mystery. The unknown. The dark. The black suits and black glasses help the Men in Black create an air of anonymity and unknown about themselves. We don't have to dig too deep into our analysis to see this at play. Zed spells it out for us in the speech he gives when Jay's putting on his black suit for the first time:

ZED: From now on, you'll have no identifying marks of any kind. You will not stand out in any way. Your entire image is crafted to leave no lasting memory with anyone. You are a rumor, recognizable only as déjà vu and dismissed just as quickly. You don't exist. You were never even born. Anonymity is your name, silence, your native tongue. You are no longer part of the system. You are above the system, over it, beyond it. We're "them." We're "they." We are the Men in Black.

The last word in the speech is "black" and the way he emphasizes it suggests that all of these qualities, "no identifying marks," "anonymity," "déjà vu," and "silence," are encompassed in the color. In this anonymity, the Men in Black can pretend to be whomever they'd like, from FBI agents to health inspectors to INS agents. They operate totally in the metaphorical dark, and the black suits drive that home.

And we can't forget that, when your job includes delivering alien squid babies and blasting your way out of alien bug guts, black cuts down considerably on your dry-cleaning bills. Man, that stuff is expensive.